This invention relates to gas turbine and steam turbine combined cycle electric power generating plants and to control systems for and methods of controlling the operation of same.
In a combined cycle electric power generating plant employing one or more gas turbines and one or more steam turbines, the hot exhaust gas from each gas turbine is typically supplied to a boiler or steam generator for providing heat for producing the steam which drives the steam turbine or turbines. The various turbines drive one or more electric generators which produce electricity which is supplied by an electric utility system to various industrial, commerical and residential customers. In some combined cycle plants, further heat is supplied to the steam generator or generators by means of additional or supplemental burner mechanisms. In either case, such combined cycle plants are relatively complex in nature and a relatively large number of sensors and actuator mechanisms are provided for adjusting, regulating and monitoring the operations of the various turbine, generator and burner units and the auxiliary equipment normally associated therewith. Other arrangements of gas and stream turbines, steam generation sources and waste heat recovery apparatus can be employed in combined cycle plants.
One of the attractions of combined cycle plants is that in the intermediate power generation capacity range, for example 200 megawatts to 400 megawatts, power can be economically generated for base, intermediate or peaking generation. Further, the delivery lead time to obtain operational combined cycle power genration capacity can be significantly less than that in the case of fossil or nuclear base load steam plants. Thus, there is a significant market in the electric power industry for combined cycle plants. More information on combined cycle plants cna be obtained in prior patents and publications such as an article "Combined-Cycle Plant Serves Intermediate System Loads Economically" by P. Berman and F. Lebonette in the November 1970 Westinghouse Engineer, an article "A Combined Cycle Plant For Intermediate System Loads" presented by P. Berman and F. Lebonette at the 1970 Joint Power Generation Conference in Pittsburgh, Pa., and an article "Operating Concept For A 240 Megawatt Combined Cycle Intermediate Peaking Plant" presented by P. Berman to the ASME in 1971.
Generally, it is desirable to develop power plant manufacturing techniques and power plant structure which leads to reducing delivery lead time for electric power plants in general and combined cycle plants in particular. Reduced delviery time enables better power industry planning for installed generation capacity since it can proceed with greater currency. One approach to realizing better power plant construction with reduced lead time is that which involves substantially increased factory participation in the manufacture and assembly of power plant apparatus as set forth in the above noted case Ser. No. 399,582. The present disclosure embraces aspects of the power plant manufacturing and delivery process relating to control system testing as an integral part of the process.
Key tests put on the adequacy of an electric power plant are its availability and its reliability, i.e., whether it is actually available for safe startup and operation from standby and whether once operational it will continue to operate safely to produce demanded power. The significance of the availability and reliability factors increases with increasing savings or peaks of power demand and with increasing congruity between installed power generation capacity and user power demand. The requirement is that power always be safely and inexpensively available on demand, without a requirement for excessive operating costs nor excessive capital investment in power generation facilities.
Automatic coordinated plant operation can provide for better plant operation in various ways including:
Although automatic coordinated operation has been applied to fossil steam power plants with electric analog control systems or with digital computer control systems as set forth in copending patent application Ser. No. 413,275, filed by T. Giras et al on Nov. 6, 1973 and assigned to the present assignee or to boiling water reactor plants as set forth in U.S. Pat. No. 3,778,347, no known prior art discloses a progressive application of coordinated control concepts to combined cycle plants to achieve computer control techniques and hybridization techniques as applied to the controls for a power plant can also lead to better plant reliability, availability and efficiency. For example, a digital computer/analog hybrid system has been developed for controlling gas turbines as set forth in the aforementioned Ser. No. 319,114. Further, a digital computer system with limited analog backup and electrohydraulic interface equipment has been developed for controlling steam turbines as set forth in coassigned applications Ser. No. 319,115 and Ser. No. 408,962. However, none of this nor any other known prior art pertains directly to combined cycle plants.
As can further be appreciated, it is desirable to operate a combined cycle power plant so as to obtain improved or maximum efficiency (minimum heat rate) at each operating level or electrical power level. In other words, it is desirable to improve or minimize the total fuel consumption rate at any given electrical power output level for the plant as a whole. It is also desirable more particularly to provide a plant in which the control system automatically coordinates the settings of the fuel valves and throttle valves for the various turbine and burner mechanisms to automatically accomplish this purpose with a minimum of reliance upon a human operator. It is further desirable to provide a plant having an automatic control system which enables the amount of generated power to be changed from one level to another in the shortest possible length of time for various different operating conditions.
The various plant apparatus and control systems heretofore proposed for use in connection with combined cycle and other electric power generating plants leave much to be desired in the way of accomplishing these objectives.